After calling perf_event_open() with cpus == -1 and the inherit bit,
using mmap on the perf file descriptor to create a ring-buffer fails
with EINVAL. This behavior wasn't previously documented in the man
page and is caused by the following lines in the perf_mmap function in
kernel/events/core.c:
/*
* Don't allow mmap() of inherited per-task counters. This would
* create a performance issue due to all children writing to the
* same rb.
*/
if (event->cpu == -1 && event->attr.inherit)
return -EINVAL;
Signed-off-by: Mikołaj Kołek <kolek.mikolaj@xxxxxxxxx>
---
man/man2/perf_event_open.2 | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/man/man2/perf_event_open.2 b/man/man2/perf_event_open.2
index 2f345ff5b..15a5972d0 100644
--- a/man/man2/perf_event_open.2
+++ b/man/man2/perf_event_open.2
@@ -1025,6 +1025,10 @@ .SS Arguments
.I read_format
values, such as
.BR PERF_FORMAT_GROUP .
+Additionally, using it together with
+.BR "cpu == -1"
+prevents the creation of the mmap ring-buffer used for
+logging asynchronous events in sampled mode.
.TP
.I pinned
The
--
2.45.2
